I live in the southern hemisphere near Melbourne, Australia (about 35 degrees south latitude). I have some visitors from the USA (Colorado) who say they noticed that the face of the moon looks different in the southern hemisphere than from their vantage point in the northern hemisphere. This view is not from a telescope/binoculars but just unaided eyesight. Would the moons face be noticeably different from northern and southern hemispherical (unaided) view points?

I'm not surprised they noticed a difference in the appearance of the moon. Had they tilted their head and looked at the Moon upside down, it would have looked normal (to them anyway). In short, the moon looks upside down in the southern hemisphere (or in your case the moon would look upside down in the northern hemisphere). I noticed exactly the same thing on my first trip to southern hemisphere.

To understand why this happens, imagine for simplicity that the orbit of the Moon was exactly in the same plane as the Earth's equator. From the northern hemisphere, the Moon is in the southern sky because that's the direction of the Earth's equator. In the southern hemisphere the situation is reversed. Now imagine that you are standing on the equator. The Moon would be directly overhead. First face north and look straight up at the Moon. It should look like it does in Australia. Now turn and face south and look at the Moon. You are now looking at the Moon flipped from how it looked when facing north. This is how the moon looks in the northern hemisphere to your American friends.

The equator is a special place because the moon is overhead (at least in our thought experiment), and there's no preferred viewing direction. At higher or lower latitudes there is a preferred direction, namely the one when you're standing on your feet and not your hands, so you really only see the moon in one orientation.

About the Author

Laura Spitler was a graduate student working with Prof. Jim Cordes. After graduating in 2013, she went on to a postdoctoral fellowship at the Max Planck Institute in Bonn, Germany. She works on a range of projects involving the time variability of radio sources, including pulsars, binary white dwarfs and ETI. In particular she is interested in building digital instruments and developing signal processing techniques that allow one to more easily identify and classify transient sources.

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